Hereditary startle disease (STHE, also known as hyperekplexia and congenital stiffman syndrome) is a rare, autosomal dominant disorder that is characterized by severe hypertonia in the neonatal period, and by a persistently exaggerated startle response to sudden, unexpected acoustic or tactile stimuli. STHE responds dramatically to nonsedating doses of the benzodiazepine clonazepam. Multipoint linkage analysis with nine polymorphic microsatellite markers in four large STHE families unequivocally assigns the STHE gene to chromosome 5q and indicates that it is flanked by the markers CSF1-R and N5.64/2G10, which are themselves very tightly linked Of interest, this region of 5q contains several important genes that encode glutamate, adrenergic, and gamma-aminobutyric acid receptor components. The goal of this proposal is to create a high-resolution physical map of the immediate STHE region, and to identify candidate genes contained therein. Initially, we will develop a panel of new, sequence-tagged markers for the STHE region from irradiation-reduced somatic cell hybrids containing fragments of chromosome 5q as their only human DNA. After placing these markers on a 5q map by analysis of their retention patterns in a panel of radiation hybrids, we will use them to identify yeast artificial chromosomes (YACs) from a large-insert library; the YACs will then be used to construct a contig of the STHE region. Several complementary mapping strategies will be employed including long-range restriction mapping with pulsed-field gel electrophoresis, fluorescent in situ hybridization of interphase nuclei, and meiotic mapping with new polymorphic markers in an expanded set of STHE pedigrees. The project will reach completion with the identification of STHE candidate genes on the contig by screening of brain cDNA libraries. Subsequent experiments will include analysis of candidate genes for STHE-specific mutations, determination of the STHE cDNA sequence, and analysis of the effect of mutations on the function of the STHE gene product. Historically, single-gene diseases have served as useful models for the investigation of basic biological processes. We believe that understanding the normal, function of the STHE gene and how it is impaired by specific mutations will yield unique insights into the regulation of muscle tone and the startle response in humans.